1. Field of the Invention
The present invention relates to an exhaust gas recirculation system of an internal combustion engine.
2. Description of Related Art
Internal combustion engines typically include an exhaust gas recirculation (EGR) system to recirculate a controlled portion of the engine exhaust gas into an engine intake manifold in order to provide a reduction in NO.sub.x emissions. Typically, a control mechanism including an EGR valve is provided to vary the EGR rate according to one or more sensed conditions, such as engine coolant temperature, air charge entering the intake manifold, and engine speed. A stepper motor driven EGR valve has been employed in an exhaust gas recirculation system wherein stepper motor steps are calculated primarily as a function of engine speed and air charge. Control of the EGR stepper motor without accounting for the temperature of the exhaust gas flowing through the EGR system can produce errors in control of the EGR valve and resulting EGR mass flow rate.
An object of the present invention is to provide an estimated EGR exhaust gas temperature to improve control of an EGR valve to provide a desired EGR mass flow rate.